Field
Embodiments of the invention relate to wireless communications networks, such as a heterogeneous network (HetNet).
Description of the Related Art
In wireless communications, a heterogeneous network (HetNet) refers to a network where different types of nodes are participating in the communication. More specifically, HetNet scenarios in cellular communication systems are scenarios with different types of base stations (BSs). For example, besides the most common rooftop or mast-located macro BSs, a HetNet scenario in 3GPP may include deployment of small outdoor pico BSs and even smaller home (or femto) BSs.
Compared to macro BSs, the pico and femto BSs have lower transmission power—e.g. 3GPP defines maximum transmission power for pico BS and femto BS to stay within ±2 dB from a rated output power of 24 dBm and 20 dBm, respectively. These values are per carrier and correspond to a single antenna port—doubling the number of antenna ports, for example, reduces the limit by 3 dB. For a macro BS, the output power is limited by spectrum regulations; a typical value is 46 dBm. One purpose behind deployment of pico and femto BSs is to bring higher data rates to user equipment (UEs) that is connected to them, and to offload traffic from the macro BSs. However, interference between BSs may occur.
There are several scientific papers discussing interference management in femtocell networks. Although femto downlink power control (DLPC) has been applied to reduce interference to macro downlinks, femto DLPC has never been optimized in a cross-direction time division duplex (TDD) context.
There are two conference papers that discuss cross-direction macro/femto interference. The use of opposite-direction frame structure to enhance capacity is discussed in H. Wang and D. Hong, “Capacity Enhancement Using Reversed-Pair TDD Frame in OFDMA Femto-Cell Systems,” Vehicular Technology Conference Fall (VTC 2009-Fall), September, 2009 (hereinafter, “Capacity Enhancement”). A discussion of macro interference to femto uplink transmission is also discussed in C. That and P. Popovski, “Interference Cancelation Schemes for Uplink Transmission in Femtocells,” GLOBECOM Workshops (GC Wkshps), December, 2010 (hereinafter, “Interference Cancelation”). However, both papers propose to use interference cancellation via data sharing through a backhaul connection.
Discussion concerning controlling communication between a macro BS and a femto BS is provided in Kwon et al., US 2010/0097965 (hereinafter “Kwon”), and Kim et al., U.S. 2010/0322180 (hereinafter “Kim”). Kwon is directed to a femto BS measuring radio environment around itself and reporting to a macro BS, which responds with orders to the femto BS on how to organize its transmissions. Kim is similar, except that the BSs are specifically meant to exchange scheduling information.